Which words in the sentence are the complete infinitive phrase?
because she had never baked a cake before, sharon decided to follow the recipe carefully.
a. because she had
b. sharon decided to follow
c. baked a cake before
d. to follow the recipe carefully

Infinitive phrases starts with infinitives that is, “to” added by a simple verb and can be used as nouns, adjectives or adverbs. In the case of including a main clause in the sentence, infinitive phrase separates it with comma. In the sentence: Because she had never baked a cake before, Sharon decided to follow the recipe carefully. A main clause is put first ‘Because she had never baked a cake before’ then a comma is added, so that means the infinitive phrase is ‘d. to follow the recipe carefully’.